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    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
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    <script>
        /**
         * ... | push
         * push会改变原数组，返回结果是追加后数组的长度
         */
        const arr = [1, 2, 3]
        console.log(arr.push(5)); // 4
        console.log(arr); // [1, 2, 3, 5]
    </script>
</body>
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